Page 288 - Programming Microcontrollers in C

Timer Operations 273

/* The initialization portion of the program */
TCTL2.EDG1B=ON; /* capture falling edge only */
OC1M.OC1M7=ON; /* sent OC1 out to PA7 */
OC1M.OC1M5=ON; /* couple OC1 to OC3 */
TMSK1.OC3I=ON; /* enable the OC3 interrupt */
TMSK1.IC1I=ON; /* enable the IC1 interrupt */
OC1D.OC1D5=ON; /* turn on OC3 with OC1 */
TCTL1.OL3=ON; /* toggle OC3 when OC3 occurs */
PACTL.DDRA7=ON; /* make OC1 an output to PA7 */
TOC1=TCNT+PWM_period; /* set OC1 */
TOC3=TOC1+PWM_count; /* set OC3 time on */
cli(); /* enable the system interrupts */
/* the applications portion of the program */
FOREVER
{ /* All of the numbers used below are derived
in the text */
if(old_motor_speed!=motor_speed)
{
motor_period=30000000Lu/motor_speed;
old_motor_speed=motor_speed;
PWM_count= ((motor_speed+12528)/63)*8;
PWM_count=limit(PWM_count);
}
if(tick)
{
tick=FALSE;
delpc=(3809500Lu/motor_period);
delpc=delpc*
(motor_period-measured_period)/
motor_period;
PWM_count-=delpc;
PWM_count=limit(PWM_count);
rpm=30000000L/measured_period;
}
/* input the new motor speed */
}
}

/* functions of the main program */